import threading
import time

import global_var as glo

def fun():
 while 1:
     glo.set_value('start', False)
     print(glo.get_value('start'))
     time.sleep(2)
     glo.set_value('start', True)
     print(glo.get_value('start'))
     time.sleep(2)

t = threading.Thread(target=fun) # 必要
t.start()
